It is fairly well established that, over time, human skin is ravaged by the effects of age, poor nutrition, exposure to sunlight and other harsh external factors. It is also fairly well established that applying topical compositions including nutrients (such as vitamins A, B, C, D, E and K and their related molecules and derivatives), UV protectants, moisturizers and anti-oxidants for protection and repair of the skin is often the best way to administer relatively copious amounts of select healing and protectant substances without adversely affecting internal tissues. However, providing topical compositions comprising [a] beneficial mixtures comprising [b] effective quantities of these ingredients, in a form which will [c] be skin permeable and bioavailable, yet [d] found pleasing to a consumer from a variety of aesthetic considerations including smell, feel, color, ease of application; [e] retain its beneficial quantities for an adequate amount of time, i.e. shelf-life; and [f] be commercially viable, i.e. cost-effective, is a task which is part artistry, part chemistry and has been for literally thousands of years.
In particular, certain of the most desirable skin nutrients, such as 1-ascorbic acid, are very easily oxidized and thus highly sensitive to pH and UV radiation, among other factors, thereby severely limiting the excipients and co-ingredients with which they may be delivered and still remain beneficial. Additionally, 1-ascorbic acid is most biologically active in aqueous form, Traikovich, S. S., Use of topical ascorbic acid and its effect on photodamaged skin topography. Arch. Otolaryngol. Head Neck Surg. 125, 1091-1098, 1999. which is unfortunately also the form in which it is most susceptible to oxidation and shortened shelf life, rapidly degrading and turning brown, rendering topical products aesthetically displeasing and commercially useless. These disadvantages, i.e. rapid product discoloration, short shelf life, rapid oxidation, have made it difficult to provide a topically administered aqueous skin composition incorporating 1-ascorbic acid.
Non-aqueous delivery vehicles incorporating 1-ascorbic acid suffer from other disadvantages including miscibility, product release and absorption, and messy residue. Trying to stabilize vitamin C by use of microencapsulation in an aloe gel base adds considerable complexity and expense to skin rejuvenation products. Furthermore, deposition of the 1-ascorbic acid payload into the skin may be very difficult to achieve in doses which are optimal for a therapeutic response, i.e. 30-40% higher than normal tissue levels.
Retinoids, which are derivatives of vitamin A, are another subset of nutrients which are highly beneficial to the health and appearance of skin, but which are also highly subject to oxidation and inactivation by sunlight, particularly retinoic acid.